Conventionally, various devices for producing a masking sound based on an input sound to make the sound from which the input sound originates, difficult to be hardly heard, such as a sound masking device have been proposed. In the device of Patent Document 1, for example, an environmental sound is input to a sound inputting section, and an environmental sound signal indicating the waveform of the environmental sound is analyzed. Based on a result of the analysis, the device of Patent Document 1 produces a specific generated sound signal. In this case, the device of Patent Document 1 produces the generated sound signal so that a person hears the environmental sound and a generated sound output from the device as a mixed sound (sound which is not uncomfortable) of a specific mode.